Distribution transformer having a molded insulative casing and oil dielectric



1966 M. 1. ZWELLING ETAL 3,234,493

DISTRIBUTION TRANSFORMER HAVING A MOLDED INSULATIVE CASING AND OIL DIELECTRIC Filed June' 17, 1963 3 Sheets-Sheet 1 In" I l"" 'II I L "I 1 INVENTORS. M4K7'7/V I. Zd/iAL/A z usiir 2555/? BY I ig M ttarney Feb. 8, 1966 M. x. ZWELLIMG ETAL. 3,234,493

DISTRIBUTION TRANSFORMER HAVING A MOLDED INSULATIVE CASING AND GIL DIELECTRIC 3,234,493 DISTRIBUTION TRANSFORMER HAVING A MOLDED INSULATIVE CASING AND 01L DIELECTRIC Martin I. Zwelling and Hubert Reher, Zanesville, Ohio, 'assignors to McGraw-Edison Company, Milwaukee,

Wis., a corporation of Delaware Filed June 17, 1963, Ser. No. 288,183 12 Claims. .(Cl. 33694) This invention relates to electrical distribution transformers.

For many years electrical power distribution transformers have conventionally been constructed with a metallic cylindrical casing enclosing a core and coil assembly immersed in oil within the casing. The asymmetry between the core and coil assembly and the cylindrica'l metallic casing necessitated a much greater volume of transformer oil than was required for purposes of insulation, and the weight of the extra oil and of the metallic casing limited the kva. 'size of the transformer that could be mounted on a pole. The metallic casing, which is usually at ground potential, necessitated expensive porcelain insulating bushings where the high voltage leads enter the casing. Further, the metallic casing often resulted in transformer outages when birds, squirrels, or other animals resting on the mettallic casing contacted exposed electrically live parts and introduced problems of safety to linemen resulting from touching the bare end of an electrically energized lead to the metallic casing when changing out a transformer. The transformer oil in such conventional units often became contaminated and lost its dielectric strength, due to breathing at the cover sealing gasket, and further the metallic tank itself often rusted or corroded after relatively few years of service, particularly in locations adjacent bodies of salt water.

Encapsulated transformers are also known wherein the transformer core and coil assembly is completely impregnated in an insulating resin so that theoretically no voids remain in the interior, moisture cannot penetrate into the interior, and corona will not be generated in service. However, different rates of thermal expansion between the core and coil assembly and the encapsulating resin freqeuntly resulted in voids and cracks in the encapsulating jacket which reduce the dielectric integrity of the encapsulating material and give rise to corona, and further the heat dissipating characteristics of such encapsulated transformers are so poor that it has been practicable to construct them in only the smaller kva. s1zes.

It is an object of the invention to provide a distribution transformer and its method of construction which is substantially smaller in volume and lighter in weight than a conventional distribution transformer having a metallic oil-filled casing but which has dielectric strength and thermal characteristics comparable to units having metallic oil filled casings. It is a further object to pro- .vide such a distribution transformer which utilizes a considerably smaller volume of insulating dielectric than a conventional unit having a metallic casing.

It is another object of the invention to provide such a small size, light weight distribution transformer which has excellent insulating and cooling characteristics and also eliminates the expensive insulation bushings and the possibility of outages resulting from birds and animals short circuiting between exposed live parts and the transformer casing. A further object is to provide such a distribution transformer which eliminates the possibility of contamination of the insulating dielectric and of corrosion of the transformer casing.

United States Patent Ofiice Still another object of the invention is to provide a distribution transformer which is comparable in size and weight to completely encapsulated units but eliminates the problems inherent in encapsulated units such as poor heat dissipation and low dielectric strength due to cracks and voids in the resin jacket.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIGS. 1 and 2 are elevation and plan views respectively of a preferred embodiment of the invention;

FIG. 3 is a view similar to FIG. 1 with the front shell removed to show the internal construction;

FIG. 4 is a view taken on line 44 of FIG. 2;

FIG. 5 is a view taken on line 5-5 of FIG. 4; and

FIG. 6 is a detail sectional view through the pressure relief and oil filling means of the preferred embodiment.

Referring to the drawing, a generally U-shaped mounting or hanger bracket 10 of channel cross section is adapted to support the form-fitted distribution transformer 11 of the invention on a wooden power pole (not shown) or other supporting structure. Mounting bracket 10 preferably has upper and lower horizontal legs 12 connected by a vertical cross-piece 113 which may have a plurality of keyhole-shaped apertures 15 adapted to fit over the heads of bolts (not shown) extending through the pole. The legs 12 and cross-piece 13 are preferably metallic channels of suitable material such as aluminum. A rod 16 may be welded to the upper bracket leg 12 to facilitate lifting. The form-fitted transformer has an outer cas ing 18 of suitable weatherresistant and temperature-resistant insulating material such as a polyester resin reinforced with fiberglass. Casing 18 encloses a transformer core and coil assembly 19 including a closed magnetic core 21 of grain oriented magnetic strip and cylindrical coils 22 surrounding the winding legs of magnetic core 21. The coils 22-may either be wound directly on the winding legs of the core 21 in a manner well known in the art, or the coils 22 may be separately constructed and the magnetic strip laminations of the magnetic core 21 inserted through the coils 22 to construct the core and coil assembly 19. Preferably magnetic core 21 is constructed of a plurality of magnetic strips 23a, 23b, 23c, 23d and 23a of different width to provide a cruciform cross section. The core and coil assembly 19 is immersed in an insulating dielectric fluid 24 contained within casing 18, and preferably dielectric fluid 24 is an oil having a flashpoint of approximately 430 F. and a firepoint of approximately 470 F. and having a higher dielectric strength than conventional transformer oil, one such oil suitable for our invention being sold under the trade designation Thermol #350X by the Sonneborn Chemical and Refining Company.

Casing :18 preferably includes two similar, opposed, front and rear hollow shells 27F and 27R respectively abut-ting at their peripheral edges and joined together at their abutting edges in surrounding relation to the core and coil assembly 1? by a suitable bonding material such vas epoxy resin. An outwardly extending flange 28 extends around the periphery of each shell 27, thereby providing a relatively wide area of abutment between the shells 27F and 27R at their peripheries and resulting in a liquid-tight bond therebetween. Metallic or non-conductive plastic channel members 29 fit over the abutting peripheral flanges 28 of the front and rear shells 27F The shells 27F and 27R are preferably molded to a configuration closely conforming to that of the contour of the core and coil assembly 19 by the well known flex- Fatented Feb. 8, 1966.

i-ble pressure forming, or vacuum bag process. Each shell 27 is molded with two semi-cylindrical ooncavities 31 complementary to the coils 22 and connected at their ends by depressions 32 generally complementary to and adapted to receive the yokes of the magnetic core 21. The depressions 32 are partially defined by upper and lower wall portions 34 extending generally horizontally from the peripheral flanges 28 at the upper and lower edges of shells 27F and 27R. Wall portions 34 of rear she'll 27R are contiguous the web portions of the channel cross section upper and lower legs .12 of the U-shaped hanger bracket 10. The shells 27F and 27R also include relatively shallow wing portions 35 extending horizontally outwardly from the depressions 3 1 and 32 over the entire height of shells 27F and 27R. The wing portions 35 of the abutting shells 27F and 27R form generally planar, shallow cooling fins for the transformer.

A protective coating of suitable resin, which may be a mixture of resins including an epoxy resin, is provided, preferably by spraying, on the interior and the exterior of each of the shells 27F and 27R, and preferably the exterior coating is sprayed to a greater thickness to insure high resistance to weather.

The core and coil assembly 19 is supported directly from the hanger bracket 10. Metallic core clamps 38U and 38L are disposed against the upper and lower yokes of magnetic core 21. Each core clamp 38 is generally L-shaped with a horizontal portion disposed against the narrowest magnetic ribbon 23, a short vertical leg 39 which abuts against a side face of the second narrowest ribbon laminations 23d with a piece of suitable insulation 40 disposed therebetween, and a longer vertical leg 42 which abuts against a side face of the widest magnetic ribbon laminations 23a with a piece of suitable insulating material 43 disposed there/between. A pair of spaced apart nuts 44U are welded to the upper core clamp 38H, and a pair of spaced apart nuts 44L, having greater axial length than the nuts 44U, are welded to the lower core clamp 38L. Flat metallic pressure plates 46 having a pair of clearance apertures (not shown) therein are cemented to the internal surface of wall portions 34 of rear shell 27R before the peripheral flanges 28 of the two shells are joined together. Clamping bolts 47 extend through aligned clearance apertures in the ends of hanger bracket legs 12, in wall portions 34 of rear shell 27R, and in the pressure plates 46 and are threaded within the nuts 44 welded on core clamps 38U and 38L. Jam nuts 49 threaded on clamping bolts 47 and against the pressure plate 46 rigidly afiix bolts 47 and thus the core and coil assembly 19, to the hanger bracket 10. It will be appreciated that the bolts 47, nuts 49, and pressure plates 46 constitute means for clamping the wall portions 34 of rear shell 27R rigidly to bracket 10. During assembly the clamping bolts 47 are adjusted within the nuts 44U to support the core and coil assembly 19 as close as possible to the top of the shell 27R, and final clamping of core and coil assembly 19 to hanger bracket is accomplished by tightening the clamping bolts 47 within the nuts 44L and the jam nuts 49 on the clamping bolts 47. Elongated spacer strips 50 of suitable insulating material such as maple wood are disposed between the coils 22 and the wall portions defining the semicylindrical conca'vities 31 to center the coils 22 within the concavities 31. The spacer strips 50 are held in position by suitable cement which may be an epoxy resin.

Since the entire weight of the transformer core and coil assembly 19 is supported directly from the hanger bracket 10, the casing 18 need support only the weight of the shells 27 and the minimal amount of insulating dielectric 24 between the core and coil assembly 19 and the shells 27 which cl-osel-y conform in configuration but are spaced from the core and coil assembly 19. It will thus be appreciated that the casing '18 can be of substantially rduced strength and weight in comparison to the conventional cylindrical metallic transformer tank. Further,

such decreased amount of insulating dielectric greatly reduces the size and weight of the transformer in corn parison to a conventional oilfilled unit having a cylindrical metallic casing while retaining comparable electrical and temperature rise characteristics. For example a 15 kva., 1200-/240 volt distribution transformer in accordance with our invention is 35% smaller and 25% lighter than an oil-filled unit of equal rating having a metallic casing.

Each core 22 contains a primary winding 52 and a secondary winding 53 separated by a high-low insulating barrier 54 (see FIG. 5'). Corrugated insulating members 56 disposed within the primary winding 52 and secondary winding 53 form cooling ducts for the upward convection circulation of dielectric liquid 24. During assembly the core and coil assembly 19 is baked in an oven for three hours at approximately 275 F., and wedge-shaped members 57 of suitable insulating material such as maple wood are driven at cirournferentia-lly spaced apart positions into the barrier and into the high voltage winding to clamp the coils 22 firmly against the core winding legs. Preferably pairs of insulating pads 59 are provided within the barrier and within the transformer windings, and the wedges 57 are driven between the pads 59 to insure that the windings 52 and 53 are not damaged.

Before shells 27F and 27R are secured together, a terminal board 61 of suitable insulating material is affixed, preferably by cement, to the internal surface of the wall portion of front shell 27F which defines the lower depression 32. Thetransformer secondary connectors include metallic connector bodies 62 disposed adjacent the outer surface of front shell 27F adjacent the lower end thereof and having threaded apertures (not shown) which receive terminal bolts 64 protruding through clearance apertures in terminalboard 61 and in the wall of front shell 27F. The terminal bolts 64 may be cemented in place to hermetically seal the apertures in shell 27F through which they protrude. The connector bodies 62 exterior of casing 18 support eyebolt means 65 for clamping power line leads. After the core and coil assembly 19 is afiixed within rear shell 27R, the front shell 27F is placed over the core and coil assembly, and suitable lugs on low voltage leads from the secondary winding 53 are affixed beneath the heads of the terminal bolts 64.

A pair of semicylindrical vertically extending hollow lead pockets 67 are molded adjacent the top edge of each shell 27. Prior to assembly of the shells 27F and 27R, holes 68 are drilled in the top wall MU of the rear shell 27R axially of the semicylindrical pockets 67 so that the holes 68 communicate with the interior of the lead pockets 67 and with depression 32. Such holes are omitted in the front shell 27F. The cable leads 70 from the primary winding 52 are covered with insulation and disposed in the pockets 67 of rear shell 27R and extend through the holes 68. The cable leads 70 may be inserted within the holes 68 and secured therein by cement to provide hermetic sealing before the core and coil assembly 19 is secured to rear shell 27R. If one side of the primary winding 52 is to be grounded, the insulation may be stripped from one primary cable 70 after the core and coil assembly 19 issecured to rear shell 27R and the cable conductor swaged within a terminal (not shown). on a copper wire (not shown) brazed to hanger bracket 10.

After the abutting flanges 28 of both shells 27F and 27R have been cleaned and adhesive applied between the flanges 28 and inside the channels 29, the channels 29 are placed over the abutting flanges 28, and the channels 29 are held in place by clamping or riveting until adhesive is cured; The unit is then baked in an oven for three hours at FL, and then the temperature is raised to 250 F. for approximately nine hours. After the unit is removed from the oven, the casing 18 is filled with liquid dielectric 24 which has been heated and vacuum treated before casing 18 is filled with oil 24, and this vacuum is maintained while the casing 18 is being filled. The vacuum is drawn on, and'the'oil 24 is flowed into casing 18* through an externally threaded,.-o il-fill bushing 71 which is inserted through'a holedrilled in the upper wall portion 34U of front shell 27F and secured thereto by a conduit nut 72 and by suitable cement which hermetically seals the hole in front shell 27F. A check valve 73 communicating with oil-fill bushing 71 relieves excessive pressure within casing 18 and also permits drawing of a vacuum on the casing 18. An'externally threaded reducer bushing 74 engages internal threads within the axial bore in oil-fill bushing 71. A check valve body 77 has external threads adjacent its lower end which engage internal threads within the axial bore in reducer bushing 74. Check valve body 77 has upper and lower axial compartments 78 and 79 connected by a reduced diameter axial orifice 80. A-ball valve 81 of suitable material such as brass or stainless steel within upper axial compartment 78 is resiliently urged against the upper end of orifice 80 by a spring 82 which abuts at its other end against an adjustable, hollow, externally threaded nut 84 which engages internal threads within the upper axial compartment 7 8. Nut 84 is normally adjusted so that ball valve 81 opens the orifice 80 when the pressure within casing 18 exceeds approximately one pound per square inch. A U-shaped. member 86 of copper tubing flares putwardly adjacent its lower end and is provided with internal threads which engage external threads adjacent the upper end of check valve body 77. Copper tubing member 86 prevents water from entering the top of the check valve 73. In underground installations an extension of porous tubing or fine mesh screen (not'shown) on member 86 prevents sealing of the copper tubing member86.

It will be appreciated that the disclosed distribution transformer requires a minimum of transformer oil, incomparison to conventional units with cylindrical casings, because of the symmetry between the casings and the core and coil assembly. The elimination of oil not needed for installation purposes together with the core and coil assembly supported directly from the mounting bracket permits use' of a casing of materially reduced mechanical strength in comparison to a 'conventional'unit. 'Such'elimination. of unnecessary oil, the reduction in size 'ofthe casing, and the lighter weight material of the casing 'results in a transformer which is substantially lighter in weight than conventional units while. maintaining dielectric strength and thermal characteristics comparable to the conventional transformers." As described hereinbefore,

a kva'. transformer in accordancewith our invention is 35% smaller and 25% lighter in weight than an oil-filled -'unit of this rating'having a cylindrical metallic casing.

: It will also be appreciated that the disclosed construction eliminates the expensive primary and secondary porcelain bushings utilized on conventional distribution transformers. Further, the casing ofinsulating material bliminatesxthe possibility of outages resulting from birds and animals short circuiting between exposed live parts and the casing; it eliminates a hazard to linemen result- ;ing from touching the bare end of an electricallyenergized lead to the casing-when changing out. a transformer; and it eliminates the possibility of deterioration of the oil dueto fbreathing at the, cover gasket which :often occurs with conventional distribution transformers. .Inasmuch as the core and coil assem'bly'is immersed in an insulating dielectric liquid within the casing, there is While only a single embodiment of the invention has been illustrated and described, many modifications and surrounded by an electrical coil and yokes joined to said winding leg, a hermetically sealed casing enclosing said core and coil assembly, said casing including two similar hollow shells of insulating material complementary to and generally conforming to the contour of said coil and said yokes and also having abutting peripheral edges hermetically sealed together, liquid dielectric within said casing covering said core and coil assembly, and mounting means engaging said yokes for clamping said core and coil assembly against movement relative to said casing and in spaced relation to said shells, whereby a minimum of liquid dielectric is required within said casing.

2. An encased electrical distribution transformer comprising, in combination, a transformer core and coil assembly including a magnetic core linked by an electrical coil, a hermetically sealed casing enclosing said core and coil assembly, said casing including a pair of similar hollow shells of polyester resin reinforced with fiberglass and being complementary to and generally conforming to the contour of said magnetic core and said coil, said pair of shells having abutting peripheral edges hermetically sealed together, liquid dielectric within said casing covering said core and coil assembly, and mounting means engaging diametrically opposed portions of said core for clamping said core and coil assembly against movement relative to said casing and in spaced relation to said shells, whereby a minimum of liquid dielectric is required within said casing, and conductor means electrically connected to said coil extending through and being hermetically sealed to said casing.

3. An electrical distribution transformer comprising,

in combination, .a sealed casing, liquid dielectric within said casing, and a transformer core andcoil assembly including a magnetic core linked by an electrical coil immersed in said dielectric Within said casing, said casing includingv a pair of similar hollow shells of insulating ma vterial complementary and generally conforming to the contour of said core and said coil and having abutting peripheral edges joined and hermetically sealed together, said casing also having a shallow cooling fin communicating with the interior of said shells. formed by outwardly extending, parallel, generally planar wall portions on said pair of shells, means engaging diametrically opposed portions of said corefor clamping said core and coil assembly against movement relative to saidcasing and injspaced relation to said shells, and conductor means from said coil extending through and being hermetically sealed to said casing.

4. In an encased electrical distribution transformer, in combination, a sealed casing, liquid dielectric within said casing, a transformer core and coil assembly including a magnetic core having a winding leg surrounded by an electrical coil immersed in said' liquid dielectric within said casing,said' casing including two similar hollow shells of insulating material complementary to and generally con-forming to the contour of said core and said coil, said shells having abutting peripheral edges hermetically sealed together, a mounting bracket, mounting means extending through and hermetically sealed to said casing and engaging said core for supporting said core and coil An encased electric distribution transformercomprising, in combination, a transformer core and coil assembly including a closed magnetic core having at least one winding leg and. a coil surrounding said winding leg, a pair of similar shells of insulating material joining at their peripheral edges and jointly defining a hermetically sealed casing surrounding said core and coil assembly, liquid dielectric within said casing, said shells being complementary to and generally conforming to the contour of said core and coil assembly, whereby a minimum of liquid dielectric. is' required within said casing, said pair of shells also having outwardly extending, generally planar, parallel wall portions spaced apart av short distance and defining a shallow cooling fin communicating with the interior of said casing and with said liquid dielectric, electrical leads from said coil extending through and being hermetically sealed to at least one of said shells, a mounting bracket, and means extending through said casing and being hermetically sealed thereto for supporting said core and coil assembly directly from said mounting bracket in spaced relation to said shells and for also supporting said casing on said bracket.

6. An encased electric distribution transformer comprising, in combination, a transformer core and coil assembly including, a closed magnetic core and coil means surrounding said core, two similar hollow shells jointly defining a casing surrounding said core and coil assembly, said shells being of polymeric resin reinforced with fiberglass and having abutting peripheral edges hermetically sealed together, liquid dielectric within said casing, said shells being complementary to and. generally conforming to the contour of said core and of said coil means, whereby minimum liquid dielectric is required within said casing, electrical conductors from said coil means extending through said casing, a U-shaped bracket exterior of said casing, and mounting means engaging the legs of said U-shaped bracket and extending through said casing for supporting said core and coil assembly directly from said bracket in spaced relation to said shells, said mounting means also engaging one of said shells and supporting said casing on said bracket.

7. An encased electrical distribution transformer comprising, in combination, a transformer core and coil assembly including a closed magnetic core having a winding leg surrounded by an electrical coil, a hermetically sealed casing enclosing said core and coil assembly, said casing including a pair of similar hollow shells of insulating material complementary to and generally conforming to the contour of said coil and of saidcore and also having abut-ting peripheral edges hermetically sealed together, liquid dielectric within said casing covering said core and coil assembly, mounting means engaging diametrically opposed portions of said core forclamping said core and coil assembly against movement, relative to said casing and in spaced relation to said shells, conductor means from said coil extending through and being hermetically sealed to one of said shells, and pressure relief means including check valve means extending through a wall portion of one of said shells and being responsive to a predetermined pressure within said casing for exposing the interior of said casing to the atmosphere.

8. An encased electrical distribution transformer comprising, in combination, a transformer core and coil assembly including a magnetic core having winding legs connected by yokes and cylindrical coils surrounding said winding legs, a hermetically sealed casing enclosing said core and coil assembly, said casing including a pair of similar hollow shells of insulating material having abutting peripheral edges hermetically sealed together and concave cylindrical wall portions complementary to and spaced a slight-distance from said coils and also having -wall portions complementary to and generally conforming to the contour of said yokes, liquid dielectric within said casing covering said core and coil assembly, mounting means engaging said yokes for clamping said core and coil assembly against movement relative to and in spaced relation to saidshells, and conductor means electrically connected to said coils and extending through and being hermetically sealed to one of said shells.

9. An encased electricaldistribution transformer comprising, in combination, a transformer core'and coil assembly including a closed magnetic core having a pair of winding legs connected by yokes and coils surrounding said Winding legs, two similar hollow shells of insulating material having abutting peripheral edges and jointly defining a casing surrounding said coreand coil assembly,

said abutting peripheral edges being joined together and hermetically sealed, sa-idshells being complementary to and generally conforming to the configuration of said coils and said yokes, liquid dielectric within said casing, a U-shaped mounting bracket, said casing having wall portions adjacent the legs of said U-shaped bracket, and mounting means rigidly engaging said legs of said bracket and extending through said casing wall portions and being heremetically sealed thereto and engaging said yokes for clamping said magnetic core against movement relativeto said bracket and supporting said core and coil assembly directly from said bracket, said mounting means also holding said wall portions of said casing against said legs of said bracket and supporting saidcasing on said bracket.

10. An encased electrical distribution transformer comprising, in combination, a transformer core and coil assembly including a closed magnetic core having vertical winding legs connected by horizontal upper and lower yokes and coils surrounding said winding legs, a hermetically sealed casing enclosing sa-id core and coil assembly, said casing including two similar hollow shells of insular ing material complementary and generally conforming to the configuration of said coils and said yokes and having sidewalls disposed generally in verticalplanes and also having abutting'continuous peripheral edges joined to.- gether and hermetically sealed, liquid dielectric within said casing, a U-shaped' mounting bracket having upper and lower horizontal legs and a vertical crosspiece, Wall portions of said casing adjacent theupper and lower ends thereof being contiguous said upper and lower legs of said bracket, means for clamping said wall portions against said upper and lower legs of said bracket, mounting means engaging said upper and lower yokes for clamp.- ing said core against movement, said mounting means extending through and being hermetically sealed to said casing and rigidly engaging said upper and lower legs of said bracket and supporting said core and coil directly from said bracket in spaced relation to said shells, and conductors from said coils extending through and hermetically sealed to said casing.

11. An encased electrical distribution transformer comprising, in combination, a transformer core and coil assembly including a magnetic core having a winding leg joined to yokes and a cylindrical coil surrounding said winding leg, means for afiixing said coil rigidly on said winding leg, a sealed casing enclosing said core. and, coil assembly, said casing including two similar hollow shells of insulating material having abutting peripheral edges hermetically sealed together and concave cylindrical wall portions complementary to said coilsand also having side and top and bottomjwall portions generally conforming to the configuration of said yokes, liquid dielectric within. said casing covering said core and coil assembly, a U-shaped mounting bracket having the legs thereof contiguous said top and bottom wall portions of one of said shells, means for securing said top and bottom wall portions of said one shell to said leg portions'of said bracket, and means engaging said bracket leg portions and said yokes and extending through and hermetically sealed to said one shell for supporting said core and coil assembly directly from said bracket legs and in spaced relation to said shells.

12. An encased electrical distribution transformer comprising, in combination, a transformer core and coil assembly including a magnetic core having winding legs connected by yokes and surrounded by cylindrical coils, a hermetically sealed casing enclosing said core and coil assembly, said casing including two similar hollow shells of insulating material having abutting peripheral edges hermetically sealed together and concave cylindrical Wall portions complementary to said coils and also having wall portions generally conforming to .the configuration of said yokes, liquid dielectric within said casing covering said core and coil assembly, a U-shaped mounting bracket having the legs thereof contiguous opposed wall portions of said casing, and mounting means extending through and being hermetically sealed to one of said shells and engaging said yokes and said bracket legs for affixing said opposed wall portions of said casing to said bracket and for supporting said core and coil assembly directly from said bracket legs in spaced relation to said shells.

No references cited.

JOHN F. BURNS, Primary Examiner. 

1. AN ENCASED ELECTRICAL DISTRIBUTION TRANSFORMER COMPRISING, IN COMBINATION, A TRANSFORMER CORE AND COIL ASSEMBLY INCLUDING A MAGNETIC CORE HAVING A WINDING LEG SURROUNDED BY AND ELECTICAL COIL AND YOKES JOINED TO SAID WINDING LEG, A HERMETICALLY SEALED CASING ENCLOSING SAID CORE AND COIL ASSEMBLY, SAID CASING INCLUDING TWO SIMILAR HOLLOW SHELLS OF INSULATING MATERIAL COMPLEMENTARY TO AND GERERALLY CONFORMING TO THE CONTOUR OF SAID COIL AND SAID YOKES AND ALSO HAVING ABUTTING PERIPHERAL EDGES HERMETICALLY SEALED TOGETHER, LIQUID DIELECTRIC WITHIN SAID CASING COVERING SAID CORE AND COIL ASSEMBLY, AND MOUNTING MEANS ENGAGING SAID YOKES FOR CLAMPING SAID CORE AND COIL ASSEMBLY AGAINST MOVEMENT RELATIVE TO SAID CASING AND IN SPACED RELATION TO SAID SHELLS, WHEREBY A MINIMUM OF LIQUID DIELECTRIC IS REQUIRED WITHIN SAID CASING. 